Acrylonitrile fibers and process for producing same



Aug. 9, 1960 7 R. D. EULERQEI'AL ACRYLONITRILE: FIBERS AND PROCESS FOR konulcmc: Y SAME Filed May '20, 1958- PRIOR ART I INVENTORS ROBERTI). EULER 7 ROBERT L. TICHENOR.

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ATTORNEY U i S t P e ACRYLONITRILE FIBERS AND PROCESS non PRODUCING SAME 7 Robert D. Euler and Robert L. Tichenor, Waynesboro,

Va., assignors to E. I. du Pont de Nernours and Company, Wilmington, Del., a corporation of Delaware Filed May 20, 1958, Ser. No. 736,495

Claims. 01. 18-54) This invention relates to the preparation of acrylonitrile fibers of modified cross-sectional shape. More particularly, this invention relates to the preparation of monolithic fibers having a crenulated cross-sectional shape from copolymers of acrylonitrile by a dry-spinning process.

Fibers or filaments are readily prepared from acrylonitrile polymers by known processes which comprise dissolving the polymer in a suitable organic solvent, e.g., dimethylformamide, and extruding the resultant solution into an evaporative atmosphere. The polymer may be a homopolymer of acrylonitrile or, if desired, a copolymer of acrylonitrile with up to 15% of one or more additional monomers may be used to give filaments having improved dye depth, dye uniformity, or other desirable properties. These copolymers differ in several respects from the homopolymeric acrylonitrile polymer. For example, they are more soluble in dimethylformamide at room temperature.

The filaments so prepared are noteworthy in view of their uniformity of cross-sectional shape. The crossvsections are in the form of dog-bones or dumbbells (Rayon and Synthetic Textiles, 30, page 91, April 1, 1949). While filaments of this shape show many advantages, they are rather easily bent in the direction of the short axis of the cross-section. It is desirable for some purposes to increase the stifiness of the fiber Without increasing its cross-sectional area. One method for accomplishing this is to alter the cross-sectional shape of the fiber. I

Attempts have been made to prepare acrylonitrile fibers having modified cross-sectional shapes. For example, U.S. Patent 2,788,563 describes a process for preparing filaments having irregular or indented contours. However, the fibers described in the patent are filled with many internal voids which render them unsuitable for many purposes.

It is, therefore, an object of this invention to produce temperature from about 150 C. to about 180 C. A

gaseous medium heated to a temperature from about 180 C. to about 200 C., and containing from about 27% to about 43% by weight of the organic solvent, is passed through the spinning cell at a rate from about 50 to 75 pounds per hour. The filaments are withdrawn from the cell at a rate from about 200 to 250 yards per minute. As will be more clearly demonstrated later herein, the spinning conditions under which the Pa nt d Aug. 9, 1960 novel products of this invention are obtained must he maintained within the limits specified.

In a preferred embodiment of the process, a solution temperature between C. and C., a cell temperature between 150C. and 170 C., and an aspiration gas temperature between 180 C. and 200 C. are used. The rate of aspiration and the solvent concentration in the gaseous medium is adjusted to give good spinning continuity and good yarn uniformity accordingto the polymer and solution concentration being used.

In the figures, Figure 1 shows the crenulated crosssections of the product obtained by the. process ofv this invention. Figure 2 shows the dog-bone. shaped fila-' ments prepared from the same polymers which are .obtained by, the conventional dry-spinning processes of the prior' art. It will be noted that the filaments shown in Figure 1 all have a monolithic internal structure.

The invention will be further illustrated. but is not intended to be limited by the following examples. Proportions are given in parts by Weight unless otherwise specified.

Example I A spinning solution was prepared by dissolving 31 parts of a copolymer of 94% acrylonitrile and 6% methyl acrylate in 69 parts of dimethylformamide. The viscosity of this solution, as measured at 125 C., was 52 poises. The solution was heated to 80 C. and was forced through the orifices of a spinneret of the type described'in U.S. Patent 1,883,423 into a spinning cell as described in U.S. Patent 2,615,198 at 'a rate of 25.8 grams per minute. The spinneret had 30 orifices, each 0.11 millimeter in diameter. The walls of the spinning cell were heated to 160 C. Kemp gas, essentially a mixture of about 87% nitrogen and 13% carbon dioxide, at a rate of 40 pounds per hour and dimethylformamide vapor at a rate of 15.1 pounds per hour, were heated to 180 C. and pumped through the spinning cell in the same direction as the spinning filaments. After leaving the bottom of the spinning cell, the yarn was contacted with an aqueous finish and was then Wound on a perforated bobbin at a speed of 200 yards per minute. The denier of this spun yarn, after 'removal'of solvent and finish, was 395. Microscopic observations of crosssections of the filaments showed them to be uniformly of the type illustrated in Figure 1. They were of the shape commonly known as crenulated and contained no internal voids or bubbles.

Bobbins of the spun yarn were extracted with water and dilute aqueous solutions of dimethylformamide at temperatures between 25 C. and C. The resultant extracted yarns were then drawn to from 4 to 8 times their original length and were then relaxed 10% to 15%. The final relaxed yarns were all found to have the same cross-sectional shape as the spun yarn. Theseyarns all showed densities between 1.175 and 1.185 which showed that they had the desired void-free structure.

Example II A solution of 31 parts of a terpolymer of 93.7% acrylonitrile, 6.0% methyl acrylate, and 0.3% sodium styrenesulfonate in 69 parts of dimethylformamide was prepared and found to have a viscosity of 52 poises, as measured at C. This solution was heated to 80 C. and spun through a 30-hole spinneret of the type described in Example I into a spinning cell, also of the type described in that example. The walls of the spinning cell were heated to C., and an aspiration medium consisting of Kemp gas containing 43% dimethylforrnamide was heated to 200 C. and passed through the spinning cell concurrently with the spinning yarn at a rate of 70 pounds per hour. After treatment with an aqueous finish, thespun yarn was woundon a bobbin at a rate of 200 yards per minute. Excluding the weight of finish and solvent, the denier of the spun yarn was 395. The filaments all showed the desired crenulated cross-sectional shape and freedom from internal voids. These features persisted through extraction, drawing, and relaxation operations.

The process of this invention is not limited to the preparation of filaments from the copolymers specified in the examples but is equally applicable to producing crenulated filaments from other copolymers of acrylonitrile containing at least 85% combined acrylonitrile in the polymer molecules. The polymer may contain from 2% to of one or more .ethylenically unsaturated monomers which are copolymerizable with acrylonitrile. For example, any of the monomers mentioned in U.S. 2,436,926 or US 2,743,994 such as acrylic, methacrylic, and alpha-chloracrylic acids, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, 2- nitro-Z-methyl propyl methacrylate, methoxyethyl methacrylate, chloroethyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, dimethyl aminoethyl methacrylate, and the corresponding esters of acrylic or alphachloroacrylic acids; acryl and methacrylamides or monoalkyl substitution products thereof; unsaturated ketones such as methyl vinyl ketone, phenyl vinyl ketone, and methyl isopropenyl ketone, vinylidene chloride, vinyl chloride, vinyl fluoride, vinyl carboxylates such as vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl butyrate, vinyl benzoate, vinyl thiolacetate, and vinyl stearate, ethylene-alpha, beta-dicarboxylic acids, or their anhydrides or derivatives such as maleic anhydride, fumaric, maleic, citraconic, and mesaconic esters, N-alkyl maleimides; N-vinyl carbazcle, N-vinyl succinimide, N- vinyl phthalimide, vinyl ethers, monoolefins or substitution products thereof such as styrene, furyl ethylene, ethylene, and isobutylene may be used. In addition, the copolymers may contain from about 0.1% to about 10% of a .copolymerizable monomer having sulfonic acid or sulfonate salt groups such as allyloxyethylsulfonic acid, allylthiopropanolsulfonic acid, vinyldichlorobenzenesulfonic acid, naphthylethylene sulfonic acid, methyl styrenesulfonic .acid as well as disulfonic and amino sulfonic acids.

The concentration of the polymer in the spinning solution should be between about and and the solution should have a viscosity within the range of about 15 to 750 poises at the temperature of spinning with viscosities between about 50 and about 200 poises being preferred. The gaseous medium may be selected from any of a number of substantially inert compositions, e.g., Kemp gas, nitrogen, carbon dioxide, etc. Air may be used; however, special precautions must be taken to prevent combustion since the solvent used is flammable.

However, the combination of spinning conditions must be maintained within certain critical limits as previously indicated. The temperature of the spinning solution must be between about 50 C. and 80 C. If the temperature falls below the lower limits, unusually high pressures are required to extrude the solution and equipment breakdowns result. .If the temperature goes above 80 .C., the dog-bone shaped filaments of the prior art are produced. If the spinning cell temperature is permitted to drop below about 150 C., the filaments tend to stick together. Again at the upper limit, i.e., above 180 C., the dog-bone shaped filaments appear. The aspiration gas should contain about 27% to 43% 'by weight of the organic solvent and must be at a temperature between 180 C. and 200 C. when the gas enters the spinning .cell. At temperatures below 180 C., the filaments stick together and above 200 C., the dog-bone shaped articles appear. If the concentration of solvent in the aspiration gas is permitted to fall below about 27%., the dog-bone shaped filaments are produced. At concentrations above about 43%, the filaments become sticky and adhere to each other. The rate of flow of the respiration gas should be between 35.0 and 7.5 pounds per hour and the spinning speed in the range from about 200 to 250 yards per minute.

The products of the present invention are particularly useful in the preparation of Woven, knit, and pile fabrics to be used in the apparel trade. They allow increases to be made in the crispness of hand of such fabrics without requiring an increase in individual filament denier which would create, in some cases, an over-all coarseness in the finished fabric. Where the fibers are used in staple form and must be converted from staple to yarn by such spinning systems as the cotton system or woolen system, the fibers of this invention give improvements in hand without altering the fineness of the yarn count that may be spun. A further advantage of the fibers of our invention lies in the fact that fabrics prepared from these fibers do not show an undesirable shiny surface, which is frequently true of fabrics made from dogbone shaped filaments because of the tendency of those filaments to arrange themselves parallel to the surface of the fabric itself.

The chief advantage of the process of .our invention is that it allows the preparation of filaments of the desired shape from copolymers of acrylonitrile by a dryspinning process with only minor changes in the equipment that may be used. Other advantages will be apparent from the foregoing discussion.

It will be apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore it is not intended to be limited except as indicated in the appended claims.

We claim:

l. The process for preparing synthetic filaments having a crenulated cross-sectional shape and a monolithic internal. structure which comprises extruding a solution containing a polymer comprised of at least 85 acrylonitrile in dimethylforrnamide at a temperature from about 50 C. to about C. through a spinneret into a spinning cell heated to a temperature from about 150 C. to about 180 C., simultaneously introducing a flow of a gaseous medium heated to a temperature from about 180 C. to about 200 C. containing from about 27% to about 43% by Weight of dimethylformamide into said spinning cell and thereafter removing the filaments from said spinning cell at a rate from about 200 to 250 yards per minute.

2. The process of claim 1 wherein the flow of .said gaseous medium is concurrent with the direction of travel of said filaments in said spinning cell.

3. The process of preparing acrylonitrile filaments having a crenulated cross-sectional shape and a monolithic internal structure which comprises extruding a solution containing a polymer comprised of at least acrylonitrile in dimethylformamide at a temperature between 75 C. and 80 C. through a spinneret into a spinning cell heated to a temperature between C. and C., simultaneously introducing a concurrent flow of a gaseous medium heated to a temperature between C. and 200 C., containing from about 27% to about 43% by weight of dimethylformamide into said spinning cell at a rate from about 50 to 75 pounds per hour and thereafter removing the filaments from said spinning cell at a rate from about 200 to 250 yards per minute.

4. The process of preparing acrylonitrile filaments having a crenulated cross-sectional shape and a monolithic internal structure which comprises extruding a solution containing a polymer comprised of at least 85% acrylonitrile and from about 2% to about 15% of a ,copolymerizable ethylenically unsaturated monomer in dimethylformamide at a temperature between 75 C. and 80 C. through a spinneret into a spinning cell heated to a temperature between 150 C. and 170 C., simultaneously introducing a concurrent flow of a gaseous medium heated to a temperature between 180 C. and 200 C. containing from about 27% to about 43% by weight of dimethylformamide into said spinning cell at a rate from about to pounds per hour and thereafter removing the filaments from said spinning cell at a rate from about 200 to 250 yards per minute.

5. A process for preparing synthetic filaments havin a crenulated cross-sectional shape and a monolithic internal structure which comprises extruding a solution comprised of at least acrylonitrile, from about 2% to about 15% of a copolymerizable ethylenically unsaturated monomer, and from about 0.1% to about 10% of a copolymerizable sulfonate monomer in dimethyl: formamide at a temperature between 75 C. and 80 C. through a spinneret into a spinning cell heated to a temperature between C. and C., simultaneously introducing a concurrent flow of a gaseous medium 15 2,316,349

heated to a temperature between C. and 200 C. containing from about 27% to about 43% by weight of dimethylformamide into said spinning cell at a rate from about 50 to 75 pounds per hour and thereafter removing the filaments from said spinning cell at a rate from about 200 to 250 yards per minute.

References Cited in the file of this patent UNITED STATES PATENTS 2,637,893 Shaw May 12, 1953 2,679,450 Hampson et a1. May 25, 1954 2,764,468 Hare Sept. 25, 1956 2,775,507 Downing et a1. Dec. 25, 1956 Pam et a1 Dec. 17, 1957 

1. THE PROCESS FOR PREPARING SYNTHETIC FILAMENTS HAVING A CRENULATED CROSS-SECTIONAL SHAPE AND A MONOLITHIC INTERNAL STRUCTURE WHICH COMPRISES EXTRUDING A SOLUTION CONTAINING A POLYMER COMPRISED OF AT LEAST 85% ACRYLONITRILE IN DIMETHYLFORMAMIDE AT A TEMPERATURE FROM ABOUT 50*C. TO ABOUT 80*C. THROUGH A SPINNERET INTO A SPINNING CELL HEATED TO A TEMPERATURE FROM ABOUT 150* C. TO ABOUT 180* C., SIMULTANEOUSLY INTRODUCING A FLOW OF A GASEOUS MEDIUM HEATED TO A TEMPERATURE FROM ABOUT 180*C. TO ABOUT 200*C. CONTAINING FROM ABOUT 27% TO ABOUT 43% BY WEIGHT OF DIMETHYLFORMAMIDE INTO SAID SPINNING CELL AND THEREAFTER REMOVING THE FILAMENTS FROM SAID SPINNING CELL AT A RATE FROM ABOUT 200 TO 250 YARDS PER MINUTE. 